Electric heating unit.



H. P. BALL.

ELECTRIC HEATING UNIT.

APPLICATION FILED DEC. 21, 1912.

1,096,820, I memeama w; 1914.

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Witnesses: I Inventor:

Henr Price Ball H. P. BALL.

ELECTRIC HEATING UNIT.

APPLIOA-TION FILED 13120.21, 1912.

1,096,820, Patented May 19, 1914. I 2 SHEETSSHEET 2.

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Her'lr'g Price Ball.-

HENRY PRICE BALL, 0F LPI'J.'IIZSZEIELID, MASSACHUSETTS, ASSIGNOR TO'GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC HEATING UNIT.

Specification of Letters Patent.

Patented May 19,1914.

Application filed December 21, 1912. Serial N 0. 737,966.

To all whom it may concern:

Be it known that I, HENRY PRICE BALL, a citizen of the United States, residing at Pittsfield, in the county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Electric Heat ing Units, of which the following is a specification.

My invention relates to electric resistance heating units, and more particularly to units of that character which are made with a substantially fiat heating surface, and are suitable for various uses either independently or in connection with other apparatus.

Electric resistance heating units of this character ordinarily comprise an electric resistance element inclosed by electric insulation and an outer casing of metal. The electrio-insulation must be such as to prevent leakage of current. and short circuits and must also be such that there will be a low thermal drop between the resistance element and the casing. It is customary to use electric insulations such as mica which have a high dielectric strength and comparatively low thermal resistance. A comparatively thin body of such insulation is ordinarily sufiicient to guard against electric leakage 4 and short circuits. It is desirable, however,

that such insulation be firmly compressed between the resistance element and the metal casing of the unit in order that air which has a comparatively high thermal resistance be eliminated as much as possible and that the inclosed parts be held firmly in place.

My invention has for its object the production of a compact and rugged heating unit of the above described character in which the insulation is firmly compacted between the casing and the resistance element and will remain in this condition indefinitely. I

My invention comprises an improved heating unit of the aforesaid. character and the method of making the same.

In carrying out the method constitutingpart of my invention I inclose the resistance element and insulation in a casing formed oftwo metal plates.- In accomplishing this I first form a recess in one of the plates of substantially the shape and size as the re sistance element and insulation by applyin pressure thereto. In forming the aforesai recess a portion of the plate of substantially the same dimensions as the recess is displaced .from the plate. The resistance element and insulation are then inserted in the recess and the plates are permanently. fastened together. The structure. thus formed is then subjected to considerable pressure so that the displaced portion of the easing is forced partially back to its original position. The metal of which the casing plates are composed should be such that it Will accommodate itself readily to the aforesaid operations and it should therefore be fairly malleable. Iron or comparatively soft steel are quite suitable for this purpose.

Although the recess in the casing plate may be formed in such a Way that it is more or less cup-shaped, I prefer to form such recess by partially or completely shearing the plate. This has the advantage over cupping the plate that in the subsequent compression of the unit there will-be a more direct' application of the compression forces to the parts in the casing and less distortion of the casing. The reason for this is that when the shearing operation is utilized the sides of the recess and of the displaced or projecting portion of the plate are straight, perpendicular to the face of the plate andin line with each other. In case the cuppingoperation is utilized, the sides of the recess and of the displaced portion are more or less curved thus departing from a direction perpendicular to the plate, and are obviouslynot in line with each other. In case the plate has been previously sheared,

the final compression acts only to force the displaced portion against the inclosed parts of the unit, withoutdistorting the plates of the casing. The'compressing force is therefore utilized completely in compacting the unit. On theother hand, if the plate has been cupped, the compression force resolves itself into two components one of which is normal to the plate and does useful work in compressing the unit and the other parallel with the late which does no useful work but on the contrary. distorts the plate by causing a lateral flow of the metal. As

the compressing proceeds,.the accumulation of metal due to the buckling of the sides of the displaced portion of the plate causes a large part of the com ressing force to be wasted in flattening said metal thus diminishing the actual compression'on the inclosed parts. Moreover such accumulation detracts from the appearance of the plate.

In the preferred form of my invention ll may either partially or completely shear the plate in forming the desired recess. I prefer to partially shear because the unsheared portion assists in holding the sheared portion in place. However, I may completely shear and in such case they friction of the punched out portion against the walls of the recess serve to hold it in place after the final compression of the unit.

My invention will be more clearly understood by referring to the accompanying drawing in which Figures 1 and 4 inclusive illustrate in vertical section the method constituting part of my invention; Figs. 5 and 6 illustrate a modification of the same; Fig. 7 is a plan view of a heating unit embodying my invention and Fig. 8 is a vertical section of the same.

Referring to the drawing and particularly to Figs. 1 to 4 inclusive, 10 is the plunger of a hydraulic or other press, 11 is a die coacting with the same and having an annular recess 12 formed in the upper surface thereof. The said recess is rectangular in vertical cross-section. The lower surface of the plunger 10 is shaped to fit into the recess 12 of the die 11 and for this purpose is provided with a circular recess 13 rectangular in cross-section and located at the center of the plunger. The plate 14 of iron or steel is placed in position over the die and the plunger 10 is forced against the salne whereupon the parts assume the positions shown in Fig. 2. The portion 15 is displaced from the plate 14 due to the partial shearing of the said plate. An annular recess 16 is thus formed in the said plate, the sides of which are in line with the sides of the displaced portion 15. In Fig. 3 is shown the plate 14 after the punching operation, the insulation 17 the resistance element 18 and the cover plate 19, the latter being formed of the same material and preferably of the same dimensions as the plate 14. After the parts have been assembled, they may be secured together as by riveting as shown in Fig. 7 at 20 so as to hold them firmly in position. The next step is. to permanently unite the two plates and this may be done'by welding. I prefer to spot-weld the plates at the center and at a number of points around the ed es on account of the fact that when united in this way there will be no warping such as would arise from a continuous weld due to the high temperature. The structure thus formed is then placed in the hydraulic or other press, as shown in Fig. 41 and submitted to a considerable pressure. This results in the displaced portion 15 being firmly compressed against the resistance element and insulation to force the same tightly against the plate 19.

In Figs. 5 and 6 is illustrated a modifica tion of the above described method. This consists in completely shearing the plate 14 instead of partially shearing the same. The remaining steps of the method are substantially the same as those in the other species of my invention hereinbefore described. As shown in Fig. .6 the punched out portion 15 has been partially forced back to the original position and is held in position by the friction between the same and the sides of the recess 16.

In Figs. 7 and 8 is illustrated the complete unit made by the first of the above described methods. The same comprises the casing 14, 19 with the inclosed resistance element and insulation held firmly in position by the displaced portion 15 of the plate 14.

Suitable terminals 21 may be provided. These are attached to loops 22 projecting from the resistance element 18. Insulating bushings 23 surrounding said terminals are held in place by metalsleeves 24.

Owing to the fact that the portion displaced by the punching operation is partially forced back to its original position, the insulation is firmly compressed between the resistance element and the parts of the casing and air spaces with. their comparatively high thermal resistance are eliminated. By reason of the fact that the recess in at least one of the plates is formed by the shearing operation, in the subsequent compression of the unit the force is applied in a direction such that it will not be fully applied to the inclosed parts of the unit and will not distort the plates by causing them to buckle. v

Various modifications of the above described method and article will readily suggest hemselves to those skilled in the art and are to be considered as coming within the scope of, my invention which is set forth in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is 1. The method of making an electric resistance unit which consists in displacing a portion of the metal plate to form a recess therein by applying pressure to the plate, placing a resistance element and insulation in said recess, placing a cover plate over said recess and compressing the structure thus formed to force the part of the plate displaced by the pressing operation partiallyback to its original position.

2. The method of making an electric resistance unit which consists in displacing a portion of the metal plate to form a recess 3. The method of making an electric resistance heating unit which consists in punching a recess in a metallic plate, inserting therein an electric resistance element and insulation, placing another metallic plate over the said recess, uniting the said plates and then compressing the structure thus formed to force the punched portion into close thermal contact with the inclosed parts.

4. The method of making an electric resistance heating unit which consists in shearing a metallic plate to form a recess therein, placing an electric resistance element and insulation in said recess, uniting. a cover plate to the aforesaid plate and then forcing the portion displaced by the shearing operation firmly against the insulation and heating element.

An electric heating unit comprising a pair of metallic plates, one of which is provided with an offset portion forming a recess, and an insulated resistance element within the said recess and compressed between the offset portion and the other plate.

(3. An electric heating unit comprising a pair of contacting metallic plates one of which is provided with a recess formed by displacing a portion thereof parallel with the plate, and a resistance element within said recess and compressed between tle displaced portion and the other plate.

7. An electric heating unit comprising ametallic plate provided with an annular recess formed by displacing an annular 1)0l' tion parallel with the plate, a cover plate, and a resistance element within said recess and compressed between the displaced portion and the other plate.

8. An electric resistance heating unit comprising a pair of contacting metallic 1 latcs, one of which is provided with an offset annular portion'forming on one side an annula-r recess and on the other side an annular displaced portion, the Walls of which are substantially in line with those of the recess, and an insulated resistance unit located in said recess, the two plates being secured to gether at a plurality of points.

In Witness whereof, I have hereunto set my hand this 17th day of December, 1912 HENRY PRICE BALL.

Vitnesses: i

H. B. DAVERIN, J. G. EDDY. 

